Maybe you're thinking of Goji juice? (not sure of the spelling)
My wife and her friends went crazy for that stuff for about three months and then...they all stopped drinking it.
I just typed acai into google, and the "autocomplete" function gave me choices of acai berry, acai berry treatments, and acai berry scams. Being who I am, I hit the "scam" option, and came up with 173.000 hits.
I don't know what the berries are, but...